Color picture cathode-ray tubes with secondary-emissive index stripes and electron multiplier rings on tube wall



May 3, 1966 SHOZO TAMURA ETAL 3,249,787

COLOR PICTURE CATHODE-RAY TUBES WITH SECONDARY-EMISSIVE INDEX STRIPES AND ELECTRON MULTIPLIER RINGS ON TUBE WALL Filed D60. 24, 1962 Fig;

PRIOR ART IHUEHTORS Shoao amara, Ken Ta. Kano HTTORHE) United States Patent 3,249,787 COLOR PICTURE CATHODE-RAY TUBES WITH SECONDARY-EMISSIVE INDEX STRIPES AND.

IVEVIXICITRON MULTIPLIER .RINGS Shozo Tamura and Ken Takano, Tokyo, Japan, assignors to Hitachi, Ltd., Tokyo, Japan, a corporation of Japan Filed Dec. 24, 19,62, Ser. No. 246,763 Claims priority, application Japan, Dec. 25, 1961,

1 Claim. (Cl. 313-92) The present invention relates to color picture cathoderay tubes of the type in which the position of the scanning beam is detected for the purpose of modulating the cathode-ray beam by a color signal corresponding to said position as detected.

A known method of detecting the position of the beam spot formed on the image screen by the scanning cathoderay beam is to form on the electron gun side of the image screen a regular arrangement of stripes adapted to emit light or secondary electrons upon-impingement thereon of the scanning beam, and to detect the light or secondary electrons emitted from said stripes for exterior utilization. One example of this method is the beam indexing color picture tube or so-called Apple tube announced by the Philco Company of USA. The Apple tube, as shown in FIG. 1, includes a glass face plate 1 having threecolor phosphor stripes formed on the face plate thereof and a metal back or conductive coating 3 on the back of said phosphor stripes 2. Red, green and blue phosphor stripes are arranged on said face plate 1 in a predeterminedorder and at regular intervals. Secondary-electronemitting stripes 4, for example, formed of MgO are formed at regular intervals on the electron gun side. of said conductive coating 3. Formed on the inner wall of the tube adjacent to the phosphor screen is a first conductive coating 5 of graphite or like material, which is electrically connected with the metal back 3 and has a terminal 6 coupled to a source of potential. Formed on the inner wall of the conical tube portion is a second conductive coating 7 of graphite or like material serving as a collector electrode for collecting secondary electrons emitted from the stripes 4. The second conductive coating 7 has a terminal 8 coupled to a source of potential. An insulating coating'9 is formed on the inner wall of the tube between said two conductive coatings 5 and 7.

In operation, a cathode-ray beam 10 emitted from an ON TUBE electron gun not shown impinges upon the secondaryelectron-emitting stripes 4 formed on the metal back 3 to excite them for emission of secondary electrons. On this occasion, an accelerating anode voltage is applied to the terminal 8 while a voltage slightly lower than the anode voltage is applied to the terminal 6 so that the secondary electrons emitted from the stripes 4 are collected by the second conductive coating 7 to be drawn out as a secondary-electron signal, which is utilized to inform the position of the cathode-ray beam.

In use of a cathode-ray tube of this type, the quantity of secondary electrons collected by the second conductive coating 7 is extremely small and the signal current drawn out of the coating is generally of the order of several microamperes or under. Therefore, the signal current must first be amplified so that the color switching circuit may be effectively controlled by the secondary-electron signal. Also, the secondary-electron-emitting stripes 4 may be replaced by suitable photoemissive stripes or phosphor stripes with a light detector arranged in place of the second conductive coating 7 to obtain the same function of detecting the position of the cathode-ray beam. However, also in this case, the detecting current obtained is limited necessitating the use of an amplifier.

Patented May 3, 1966 FIG. 2 is a similar cross section of one embodiment of the invention; and

FIG. 3 is a perspective view of one of the secondaryelectron-emitting wings employed in the embodiment.

Referring particularly to FIG. 2, the cathode-ray tube according to the present invention has secondary-electronmultiplier means generally indicated at 11 and arranged on the inner wall of the envelope over the area carrying a second conductive coating 7. As illustrated, the multiplier means is a two-stage multiplier including secondary-electron-emitting wings r r r r for firststage emission and those r r r r,,' for secondstage emission. The wings for the same stage are connected to each other at points about the periphery of the wings and voltages E and E are applied to the wings for the respective stages at terminals 12 and 13.

The secondary-electron-emitting wings r and r each have an annular configuration as illustrated in FIG. 3. The wings for each stage have diameters progressively decreasing along the conical wall of the evacuated envelope as the distance from the image screen increases. Each of the wings for either stage is formed of silver-magnesium or like material which is highly electron-emissive.

With the secondary-electron multiplier arranged over the inner wall carrying second conductive coating 7, secondary electrons 10' emitted from the secondary-electronemitting stripes 4 on the metal back 3 upon bombardment of the cathode-ray beam on the stripes 4 are first taken up by the first-stage wings r, which in turn emit a large number of secondary electrons, which are taken up by the second-stage wings r. The second-stage wings r thus emit also a large number of secondary electrons,

E represents the voltage applied to terminal 12, E the voltage applied to the terminal 13, E the voltage applied to the terminal 8 and E the voltage applied to the terminal 6. Thus, the wings for the second stage are held at a potential higher than those for the first stage and lower than the second conductive coating 7.

It has been found that with the arrangement described above, a signal current can be obtained which is several tens or hundreds times as large as one obtainable when the detection of secondary emission from the image screen is performed directly through the second conductive coating 7 as before.

In case the secondary-electron-emitting stripes 4 formed on the phosphor screen are replaced by stripes formed of CdS or like material, which emits light when bombarded by the cath'ode-ray beam, the wings for the first stage are coated with silver, cesium or other material which emits secondary electrons when irradiated by light, whereby the secondary electrons emitted by the wings for the first-stage are multiplied by the wings for the second stage in the same manner as described hereinbefore in connection with the case where the secondary-electronemitting stripes 4 are employed.

As apparent from the foregoing, with the picture tube according to the present invention, the position of the beam spot formed on the image screen by the scanning cathode-ray beam can be detected with an extremely high sensitivity. This makes it possible to realize a stabilized reproduction of colored images, which is extremely important in practical applications.

The invention is not restricted to the features described above and shown in the drawing but may be varied in many ways within the scope of the appendant claim.

What is claimed is:

A cathode-ray tube of the type including a regular arrangement of secondary-emissive stripes on the image screen and means for detecting the secondary emission from said stripes caused by the bombardment thereon of the cathode-ray beam to produce a signal representing the position of the cathode-ray beam spot being formed on the image screen, comprising a multiplicity of multiplier wings arranged on the inner Wall of the evacuated envelope of the cathode-ray tube to emit a large number of secondary electrons by bombardment on said multiplier wings of the secondary electron from said stripes, and a conductive coating formed on said inner wall for collecting said secondary electrons emitted from said multiplier wings.

No references cited.

GEORGE N. WESTBY, Primary Examiner.

R. SEGAL, Assistant Examiner. 

